Field of the Invention
This invention relates to the field of medical electronics and more particularly to apparatus for treating human pain by application of an electrical stimulus with the proper current density to the body surface and the response modulated by a magnetic field to allow manipulation of the firing rate of peripheral neurons of the A-fiber and C-fiber nociceptors such that chronic and acute pain may be consistently controlled without discomfort from the stimulation.
Maurer, et., al., 1994 (U.S. Pat. No. 4,431,002) indicates that it is well known that pain can be alleviated by electrical pulses applied to the surface of the body or to electrodes implanted within the body. His invention revealed a transcutaneous electrical nerve stimulation apparatus in which the stimulus pulses are modulated in both time and intensity in a prescribed manner, the pulse amplitude and width decreasing, while the pulse repetition rate increases and vice versa. The advantage of this arrangement is said to produce a comfortable and pleasant sensation at levels sufficient to produce muscle contraction and stimulation of deep afferent nerves to cause the release of endogenous opiates, such as endorphins, which are thought to suppress pain.
Deyo, et., al., (NEJM) concluded that Transcutaneous Electrical Nerve Stimulation (TENS) in patients with chronic low back pain is no more effective than treatment with placebo, and TENS adds no apparent benefit to that of exercise alone. It is apparent that such studies are done without the proper application and use of the technology. It is further apparent that technology is needed that is easier to understand and use by the operator.
The reduction of efficacy of a C-fiber input by coactivation of mechanoceptive A-fibers is the principle underlying transcutaneous electrical nerve stimulation (TENS). The mechanism involved is referred to as the xe2x80x9cGate Control Theory of Pain Perceptionxe2x80x9d (See FIG. 5). TENS involves electrical activation of mechanoceptive fibers. Mechanoceptive A-fibers are activated at lower electrical stimulation intensities than C-fibers, that is, A-fibers have a low threshold. Thus, the mechanoceptive A-fibers can be selectively activated by low intensity electrical stimulation without increasing the firing rate of C-fibers, that is, A-fibers can be selectively activated by low intensity electrical stimulation without increasing the firing rate of C-fibers. As the intensity of stimulation is increased, it is possible to activate both mechanoceptive and nociceptive fibers. Thus, there is a limit to how much stimulation can be applied in order for the current TENS to work. Patients who use TENS devices are fully aware that if they continue to increase the stimulus intensity, they have more pain, rather than less pain. The increasing pain with stimulation is because of C-fiber activation. In some cases, the intensity of stimulation required to achieve pain relief can be reduced simply by repositioning electrodes and reducing the current flux through tissues while still reaching A-fiber threshold. In other cases, it is not possible to achieve pain relief at sufficiently low intensities to selectively activate A-fibers. In these cases, pain may be increased and TENS is said to have failed. In these cases of failure, the information available suggests that TENS failure is largely due to inappropriate electrode placement and insufficient current flow or density at the point of desired stimulation.
Evidence from the literature, clinical observations and isolated neuronal cell preparation data suggest that efficacy of this device is best obtained by high frequency, continuous stimulation with high current density in the area of stimulation. Pacing of A-fibers along with simultaneous suppression of C-fiber firing provides reliable control of pain syndromes. For the efficacy of the invention to be realized, a quadripolar array of positive and negative electrodes are arranged in quadrilateral array such that the positive and negative electrodes are in the proper close proximity to one another such that high current density can be obtained in the area of the nerve fiber to be paced. It is a further object of this invention to suppress the firing rates of C-fibers while increasing the rate of A-fibers. This object is accomplished by placing a Magna Bloc(trademark) device within the stimulating electrode. This device, as will be demonstrated later, dramatically controls and reduces C-fiber firing. This effect on C-fiber firing is dramatically illustrated in FIG. 6. Volunteer subjects perceived the pain threshold at two (2) times the voltage (which translates to current flow) when the Magna Bloc(trademark) device was placed over the stimulating electrodes. Through this methodology, normal firing patterns can be sent to the central nervous system, frequency coded, for a sensation of comfort rather than pain.
The device of this invention consists of 4 electrodes per unit. The electrodes consist of 4 electrodes of alternating polarity and consist of 2 positive poles and 2 negative poles. The positive and negative poles of the electrode head are aligned in substantially a single plane and are oriented in a quadrilateral configuration with positive poles oriented diagonally opposite one another and negative poles oriented diagonally opposite one another. Built into each electrode is a Magna Bloc(trademark) device U.S. Pat. No. 5,312,321 (incorporated herein by reference). This device allows maximal A-fiber stimulation without the discomfort of C-fiber pain and muscle contraction. The Magna Bloc(trademark) controls the excitability of neuromuscular units and blocks C-fiber firing.
Another object of the invention is to maintain current density sufficient to send A-fiber impulses into the dorsal horn in the area of the innervation of the C-fibers involved in the pain syndrome, in sufficient density to block C-fiber input into the central nervous system. This is accomplished by placing electrodes in the correct proximity to each other using the Magna Bloc(trademark) to control C-fiber firing when the intensity is turned up to above usual C-fiber threshold and by placing a current sensor in the midpoint between the 4 electrodes. This sensor will balance the current density by rotating monitoring of the 4 electrodes and compensating by changing the input such that current density or current flow in the skin remains constant. This circuit will have a range monitor and alarm system. Current flow will alternate every 2 seconds in electrodes in FIG. 1B to A and C to D, C to A and B to D.
It is a further purpose of this invention to have two or more such 4 electrode arrays per TENS unit.
Except as noted above, the unit uses standard TENS electronics with the following parameters: 1) the parameters are intensity of output is 0 to 100 mA, frequency 0 to 200 Hzt, pulse width 400 microseconds. The device is effective either over the dorsal columns or on afferent nerve bundle as well as over the area of pain sensation. The containment means to hold the 4 electrodes, 4 Magna Bloc(trademark) devices and current density sensor and electrode pads provides a method of therapeutically placing an alternating electrode DC frequency modulated device on the human body to relieve pain, which has well controlled current density in which C-fiber firing is controlled by a Magna Bloc(trademark) field which generates a flux field gradient in the xe2x80x9c2xe2x80x9d axis of 60xc2x0 to 70xc2x0.
This aspect may further provide repetition of these steps for additional containment bodies for attachment to the human body at additional placement positions.